1. Field of the invention
This invention relates in general to performing maintenance on air conditioning systems, and in particular to a method for removing lubricant from an air conditioning system that is to be changed from one type of refrigerant to another, the original lubricant being incompatible with the replacement refrigerant.
2. Description of the Prior Art
A transition is under way from one type of refrigerant to another type of refrigerant for air conditioning systems. The first type of refrigerant has been found harmful to the ozone layer, and is being phased out. A replacement refrigerant has been developed which is less harmful to the environment. For example, a common refrigerant that is being phased out is CFC-12, and it is being replaced by HFC-134a. As CFC-12 becomes scarce and expensive, millions of air conditioning systems will need to be converted to use HFC-134a when maintenance is required on the air conditioning system.
The two refrigerants are incompatible, as well as the oil used with them. CFC-12 uses a mineral oil as a lubricant for the compressor. The mineral oil carries chlorine from the CFC-12, thus must be removed from the system. Preferably, it should be removed down to one percent or less. Moreover, mineral oil is not a recommended or desirable oil to use with HFC-134a refrigerant.
Recovery systems are widely used now for recovering refrigerant from air conditioning systems to avoid discharge into the atmosphere. A typical recovery system has high and low pressure hoses that will tap into the air conditioning system on the high and low pressure sides of the compressor. A filter screens debris as refrigerant flows into the recovery unit. A recovery unit expansion valve and evaporator convert any liquid components to a gas. A recovery compressor compresses the refrigerant, and passes it through a receiver-drier and oil separator to a condenser. The gaseous refrigerant is condensed to a cooler liquid and placed in a storage container. The filter and receiver-drier clean the refrigerant as it passes to the storage container.
Charging units are also available for charging refrigerant into air conditioning systems. These charging systems may be stand alone or they may be incorporated with the recovery unit. A vacuum pump will be employed to evacuate the air conditioning system to a selected level after the refrigerant has been first recovered. Then the pressure difference will cause refrigerant to flow from the recovery unit storage unit, or another storage container, into the evacuated system.
In the prior art, the amount of oil removed from the air conditioning system by the recovery unit is reintroduced when recharging the systems. An oil injector is employed for the reintroduction. One type of oil injector has a line that will tap into the air conditioning system. Another line leads from the base of the oil injector to an output line of the storage container. Pressure from the storage container will apply pressure to the injector to force the lubricant into the air conditioning system.
Some oil will be recovered by the recovery unit oil separator, however considerable portions will remain in the air conditioning system. The recovery unit oil separator separates oil only due to oil droplets mixed in the refrigerant flowing as a result of the suction pressure of the recovery compressor. Also, the vacuum pump will not evacuate oil from the air conditioning system. Residual amounts will remain.
While existing recovery units adequately recover some of the oil and substantially all of the refrigerant, existing units do not have provisions for recovering the lubricant to a one percent level or less. As a result, a mechanic must remove the major components of the air conditioning system and separately clean them, in order to reach the desired level. This is a time consuming process.